Son splitting total prize money (5)
I believe the answer is:
purse
'prize money' is the definition.
(I've seen this before)
'son splitting total' is the wordplay.
'son' becomes 's'.
'splitting' means one lot of letters goes inside another.
'total' becomes 'pure'.
's' placed within 'pure' is 'PURSE'.
(Other definitions for purse that I've seen before include "Contract orally" , "Prize in boxing" , "Money holder" , "Money container" , "Knit" .)